Pressing Whites

It is early on in the 2014 vintage and we are currently spending our time and energies in pressing whites.

One way of thinking about the process of winemaking is the stepwise removal of the things we don’t want. We start with bunches of grapes, with all their stems, pips, skins, pulp and juice and when our work is done we end up with a clear liquid in a bottle. For whites, most of the transformation happens quickly, within the first 8 hours. Here’s the timeline of our Semillon from St Leonards last night.

-12 hours The harvesting equipment is taken out to the vineyard. All the bins, tractors and the mechanical harvester are fuelled up and ready to roll. In the winery the crusher, press, chiller, hoses and pumps are all set.

0 hours About an hour before the coolest time of the early morning, generally about 2am, the picking begins.

+3 hours The last of the fruit is picked and delivered to the winery. Yours truly is pacing up and down like an expectant father in the waiting room.

+4 hours We weigh all the fruit, select an appropriately sized tank and start tipping. The process is efficient and looks brutal, but the equipment is set up to complete the job with the minimum damage. That said, given that the aim of the exercise is to rip the berries from their stems, break them open and squash the juice out, there is a limit as to how gentle one can be!

Destemming is the first process. In a machine that looks like a multi-bladed propeller spinning inside a cylindrical cheese grater, all the berries are knocked off the stems. The berries fall through the holes in the grater and the stems are swept out of the machine.

Crushing happens immediately. When the berries are knocked off the stems they fall into the crusher which has a pair of ridged rubber rollers. These are set far enough apart so they do not break the pips, but close enough so that all the berries are spilt open. The mix of broken berries, pips, pulp and juice is called ‘must’ and it falls from the crusher into the open hopper of the must pump. Then it is off to the press via the heat exchanger.

At this point a word of explanation about temperature; simply put, the cooler the fruit is, the slower any oxidation will take place and the more fresh aromatics will be retained. This is why we pick in the relative cool of the night and why we then work as quickly as possible. In the heat exchanger the must is pumped through a stainless steel tube which has a larger tube enveloping it. The space between the inner, must-filled tube and the outer one is filled with ice-cold liquid which brings the temperature of the must down lower. Then it goes straight to the press.

+5 hours For all its iconic imagery, the winery press is little more than a glorified sieve. Its purpose is to separate the juice from the solids. We want to do this as quickly, yet as gently as possible. Next time you have a grape to eat, swallow the pulp and juice and just chew on the skin for a bit. After a short while you will get a harsh, drying sensation in the mouth. This is because you have broken the cell walls that contain all the tannins. When we press whites we want to avoid extracting the tannins, so wine presses are designed to get as much juice as possible with minimal harsh treatment. At first the juice simply runs out of the press, then we apply a little pressure – say 100Mb (about as hard as you can blow). If all goes well we will get ¾ of our total juice yield by this stage. For delicate white wines like Riesling we don’t even bother pressing any harder as we know we can't use the juice.

+6 hours Time to get a bit more assertive to get the last of the juice. At this stage we make what is known as a ‘cut’. The first juice, known as the "Free Run" is all out, and in one tank, so we switch to a second tank for the "Pressings". Then we set the controls to gradually increased pressures, interrupted by occasional rolls to break up the cake of skins. Our press is extremely gentle and its maximum rating is 900Mb, which is roughly what you would get under the cap of a wine bottle if you stood it on its head.

+8 hours The pressing is now finished and we have extracted all the juice we want. The Free Run and Pressings fractions are in two separate tanks and will settle out for a day to two. Now it is time to empty the skins from the press, wash all the equipment and put it away.

Obviously we are nowhere near finished and there is a huge amount of work to do before we can put anything in a bottle, but the first major steps are complete. Eight hours previously the bunches were hanging on the vine and now everything but the juice has been removed. The stems have been tipped over the fence for the cows to eat, the skins are in the compost pile and the juice is safely in tank.

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